Noise suppressor for jet engines

ABSTRACT

The disclosure of this invention pertains to an exhaust nozzle for jet engines wherein the nozzle has a generally circular outlet opening defined by an edge lying in a plane normal to the nozzle axis except at two diametrically opposite localities at each of which the edge defines a recess where the nozzle is laterally open to the ambient air. The presence of the recesses causes the jet to spread in the plane of the recesses with the effect of sound suppression in that plane.

States Patent 1191 FFowces-Williams et al.

NOISE SUPPRESSOR FOR JET ENGINES Inventors: John EirwynFFowces-Williams,

Surrey; Roy Hawkins, Bristol; Hylton Dawson, Bristol; William Smith,Yate, 31151611311 of England Assignee: Secretary of State Defence in HerBritannic Majestys Goverment of the United Kingdom of Great Britain andNorthern Ireland, London, England Filed: Nov. 23, 1971 Appl. No.:201,375

Foreign Application Priority Data Nov. 30, 1970 Great Britain 5,688/70Nov. 26, 1970 Great Britain 3,234/70 US. (11...... 239/265.27 239/265.35Int. Cl. B64c 15/04 Field of Search 239/2651 1, 265.13, 239/265.l9,265.27, 265.25, 265.35, 265.33; 181/33 HC, 33 HD References Cited UNITEDSTATES PATENTS 12/1959 Gelin et al. 239/265.17

1451 July 3, 1973 3,612,399 10/1971 Rodgers et al 239/265.l9 3,095,6977/1963 Reinhart 239/265.13 X 2,975,593 3/1961 Bauger et a1 239/265.275,153,319 10/1964 Young et a1. 239/265.19 3,344,882 10/1967 136111011 etal 239/265.13 x

FOREIGN PATENTS OR APPLICATIONS 1,301,341 8/1969 Germany 181/33 HCPrimary ExaminerM. Henson Wood, Jr.

Assistant ExamineF-John J. Love Attorney-Richard K. Stevens, Davidson C.Miller et al.

[5 7] ABSTRACT The disclosure of this invention pertains to an exhaustnozzle for jet engines wherein the nozzle has a generally circularoutlet opening defined by an edge lying in a plane normal to the nozzleaxis except at two diametrically opposite localities at each of whichthe edge detines a recess where the nozzle is laterally open to theambient air. The presence of the recesses causes the jet to spread inthe plane of the recesses with the effect of sound suppression in thatplane.

5 Claims, 9 Drawing Figures Y szavv/ Patented July 3, 1973 5Sheets-Sheet 1 Patented July 3, 1973 3,743,185

5 Sheets-Sheet 2 FIG. 3

FIG. 2

Patented July 3, 1973 FIG. 5

5 Sheets-Sheet 5 S Nd FIG. 4

Patented July 3, 1973 3,743,185

5 Sheets-Sheet 4 FIG. 7

FIG. 6

Patented July 3, 1973 5 Sheets-Sheet 5 0 .I|IIIIIIIIIIIIIIII 3 NOISESUPPRESSOR FOR JET ENGINES This invention relates to noise suppressorsfor jet engines and is concerned with the suppression of jet noise.

It is an object of this invention to provide improved means forsuppressing jet noise in a selected axis plane of the nozzle generatingthe jet. The need for this arises, for example, during the take-off of ajet propelled aircraft when, while the aircraft is at ground level, onlythe jet noise emanating in the direction parallel to the ground disturbspersons in the vicinity of the aircraft; noise emanated in the verticaldirection is of relatively lesser significance in this situation.

According to this invention there is provided an exhaust nozzle for jetengine, comprising a duct having an edge defining the discharge openingof the duct, the duct being dimensioned for the edge to lie in a planetransverse to the longitudinal axis of the duct except at two locationssituated at opposite sides of said axis where the duct is dimensionedfor the edge to define recesses at which the duct is open to ambient airin a direction laterally of said axis.

When operating the nozzle at a pressure ratio greater than 1:1,preferably greater than 2:1, the presence of the recesses causes the jetflow to spread at said opposite sides while remaining relativelyundisturbed at the remaining sides.

An observer facing the edges of the spread jet experiences a lessersound pressure level than that emitted by a jet from a comparable nozzlenot having said recesses.

Examples of this invention will now be described with reference to theaccompanying drawings wherein:

FIG. 1 is a perspective view of a jet nozzle according to a firstexample.

FIG. 2 is a side elevation of the nozzle.

FIG. 3 is an end view of FIG. 2.

FIG. 4 is a diagram for explaining the manner of measuring the noise ofthe jet from the nozzle.

, FIG. 5 is a diagram of the jet noise characteristics of the nozzle.

FIG. 6 is a side elevation of a nozzle according to a second example.

FIG. 7 is an end view of FIG. 6.

FIG. 8 is a part sectional side elevation of a nozzle according to athird example.

FIG. 9 is a section on the line IX 11X in FIG. 8.

Referring to FIG. 1, there is shown a jet nozzle for gas turbine engine(not shown). The nozzle comprises a convergent annular duct 14 ending atan edge 12 defining the discharge opening or throat. The edge 12 hasparts 13 lying in a plane 15 normal to an axis 11 being the axis of theduct, i.e., the axis defining the mean direction of flow through thenozzle. The edge 12 further includes parts 18 shaped to define tworecesses 16 situated at diametrically opposite sides of the axis 11 andat which the duct 14 is open to the ambient air. If the nozzle has theusual circular throat the flow of a jet 20 from the nozzle retains agenerally circular crosssection 21. However, the presence of therecesses 16 causes the jet to have component motions 22,22 away from theaxis ll and in the plane 26 of the diameter on which the recesses aresituated. In consequence the jet is deformed away from the circularshape into a shape 23 in which it is widened in the plane 26 and to arelatively smaller extent narrowed in the plane 27 perpendicularthereto. The amount of deformation increases with the distance from thethroat.

The deformation of the jet in the manner described has the consequencethat the jet noise in the plane 26 is less than the noise emitted by ajet from a comparable nozzle having a throat which is not recessed.Generally the noise attentuation increases with the extent of thedeformation, and the latter increases with the size of the recesses andwith the pressure ratio of the nozzle, i.e., the pressure drop acrossthe area bounded by the edge 12. The pressure drop is necessary for theestablishment of the lateral component motions 22 and a pressure ratioof 1:1 is not sufficient for this. The deformation of the jet isaccompanied by some loss in the axial thrust of the engine. The size ofthe recesses is therefor a matter of finding an acceptable compromisebetween noise attenuation and thrust loss.

In an experimental result a reduction of about 10 PNdB was achievedagainst a thrust loss of about 5 percent. The experimental nozzle,illustrated in FIG. 2 and 3, has the dimensions shown and was operatedat a pressure ratio of 3.25:1 and a gas temperature of 1,100K. The noisewas measured in the usual manner at points spaced along a line Dparallel to the nozzle axis, as shown in FIG. 4, the distance of any onepoint from the nozzle being given in terms of the angle a. The noisemeasurements are plotted as shown in FIG. 5 where the curves A, B and Crelate respectively to the noise levels in the planes 26,27 and thenoise levels of a comparable datum nozzle whose throat is not recessed.The datum nozzle, whose throat is shown at 10A on FIG. 3, was comparablein the sense that it had the same mass flow, pressure ratio and gastemperature as the nozzle 10. This equivalence occurs if the throat areaof the datum nozzle is approximately the same as the projected area, asseen in FIG. 3, of the nozzle 10.

It will be seen that the highest noise level in plane 26 (curve A) wassignificantly less than that of the datum nozzle. The highest noiselevels in plane 27 (curve B) was relatively high and may in fact byabove the curve C so that it may be said that the total radiated noisepower of nozzle 10 is not significantly different from that of the datumnozzle. The spreading of the jet occured at an angle )3 (FIG. 4) of 40to 45.

Referring to FIG. 6 and 7, there is shown a nozzle comprising a firstduct portion 114A ending at an edge 1112A and a second duct portion 114Bending at an edge 112B lying upstream of the edge 112A and wholly in aplane B transverse to the axis 111 of the nozzle. The edge 112A hasparts 113 lying in a plane 115A transverse to the axis 111 and parts 118forming two diametrically opposite recesses 116 similar to the recesses16 of the nozzle 10.

The duct portion 114A comprises two members 117 supported by links 120for movement between the operative position shown in full lines and aninoperative position shown in broken lines. The members 117 are shapedso that when they are in the operative position they form the edge 112A,including the recesses 116, between them, and in this position theportion 114A constitutes a downstream extension of the portion 11413 andthe edge 112A constitutes the controlling discharge opening of thenozzle.

The movement of the member 117 is effected by pneumatic motors (only oneshown) and during movement from the operative position the links 120cause the members'1l7 to move with a motion having a component laterallyaway from the axis 111 to bring the members clear of the edge 11213 inthe sense of not influencing flow from the latter edge. The movementalso has a longitudinal component and at the end of the movement theedge parts 113 lie in the plane 1153 of the edge 1 12B and the latter isthen the controlling discharge opening of the nozzle. The inoperativeposition is adopted when thrust is more important than noisesuppression, e.g., during cruise, as distinct from takeoff of theaircraft.

It is desirable that the flow areas of the edges 112A and 112B should bethe same so as not to change the nozzle pressure ratio when changingfrom one mode of operation to the other. It will be seen that by virtueof the convergence of the ducts ll4A,ll4B it is possible to satisfy thiscondition.

Referring to FIGS. 8 and 9, there is shown a nozzle 210 comprising afirst duct portion or shroud 214A being a cylinder having an edge 212Aparts 213 of which lie in a plane 215 transverse to the axis 211 of thenozzle and other parts 218 of which form two diametrically oppositerecesses 216. The portion 214A is supported by a part 230 surrounding asecond duct portion 214B which is convergent and coaxial with the shroud214A. The portion 2148 has a discharge opening constituted by an edge2128.

The portion 214A is supported by the portion 214B for rotation about theaxis 211 so that the recesses 216 can be moved through a range of 90between planes 226 and 227 (FIG. 9) for the purpose, for example, ofchanging from noise suppression in a horizontal plane during the groundroll part of an aircraft take-off to noise suppression in a verticalplane during low level overfiight of built-up areas adjacent the airfield.

The portion 214B has two extensions 231 positioned to close the recesses216 if the portion 214A is rotated beyond said 90 range and thereby tomake the noise suppressor inoperative.

The discharge opening of the nozzle 210 is constituted essentially bythe edge 2128. It will clear that the area of this opening does notchange during rotation of the portion 214A between positions when therecesses 216 are respectively open and closed because the diameter ofthe portion 214A is uniform over its length.

Rotation of the portion 214A is effected by a flexible cable 236 whichis wrapped around the part 230 and locally secured thereto. The ends ofthe cable are lead over pulleys 237 and secured to racks 238,239 meshingwith a pinion 240 driven by a pneumatic motor 241. The arrangement ofthe pulleys racks, pinion and motor is supported on a jet pipe 242 whichconnects the nozzle to an engine (not shown).

The portion 214A should not be longer axially than is necessary foraccommodating the recesses 216 in a position downstream of the edge 212Bas otherwise there would be a loss of the gas pressure necessary for theeffectiveness of the recesses 216 in flattening the jet.

What I claim is 1. An exhaust nozzle for a jet engine, comprising:

a first duct portion having an edge defining the discharge opening ofsaid nozzle, said edge lying in a plane substantially normal to thelongitudinal axis of said nozzle;

first and second opposed recessed portions formed in said edge of saidfirst duct portion for spreading a portion of the stream of outlet gaspassing through the nozzle substantially laterally of the main stream;

a second duct portion coaxial with said first duct portion; and meansfor rotating said first and second duct portions relative to each otherto rotate the plane of the laterally spread portion of said stream ofoutlet gas through a predetermined angle.

2. The exhaust nozzle as defined in claim 1, wherein said second ductportion comprises first and second members extending substantiallyparallel to the longitudinal axis of said nozzle, said first and secondmembers cooperating with said first duct portion to close the openingsformed by said recessed portions when said first and second ductportions have been rotated through a further predetermined anglerelative to each other.

3. The nozzle as defined in clam 1, wherein the plane of said laterallyspread portion is rotatable by the relative rotation of said first andsecond duct portions through an angle of approximately 4. The exhaustnozzle as defined in claim 1, wherein said second duct portion islocated upstream of said first duct portion.

5. Nozzle according to claim 1 wherein said second duct portion isconvergent and has at its small area end an edge defining a dischargeopening, said first duct portion is of uniform flow area and extendsdownstream of the discharge opening of the second duct portion.

1. An exhaust nozzle for a jet engine, comprising: a first duct portionhaving an edge defining the discharge opening of said nozzle, said edgelying in a plane substantially normal to the longitudinal axis of saidnozzle; first and second opposed recessed portions formed in said edgeof said first duct portion for spreading a portion of the stream ofoutlet gas passing through the nozzle substantially laterally of themain stream; a second duct portion coaxial with said first duct portion;and means for rotating said first And second duct portions relative toeach other to rotate the plane of the laterally spread portion of saidstream of outlet gas through a predetermined angle.
 2. The exhaustnozzle as defined in claim 1, wherein said second duct portion comprisesfirst and second members extending substantially parallel to thelongitudinal axis of said nozzle, said first and second memberscooperating with said first duct portion to close the openings formed bysaid recessed portions when said first and second duct portions havebeen rotated through a further predetermined angle relative to eachother.
 3. The nozzle as defined in clam 1, wherein the plane of saidlaterally spread portion is rotatable by the relative rotation of saidfirst and second duct portions through an angle of approximately 90*. 4.The exhaust nozzle as defined in claim 1, wherein said second ductportion is located upstream of said first duct portion.
 5. Nozzleaccording to claim 1 wherein said second duct portion is convergent andhas at its small area end an edge defining a discharge opening, saidfirst duct portion is of uniform flow area and extends downstream of thedischarge opening of the second duct portion.